In a variety of chemical, petrochemical and refinery processes, organic process streams, for example, light and heavy naphtha, raffinate, oxygenates etc., or waste streams are generated which contain minor or trace amounts of halogenated organic compounds as undesired by products or contaminants. These halogenated organic impurities can interfere with the recycle, disposal and/or subsequent use of the contaminated process or waste stream, for example, by poisoning catalysts or corroding process equipment, in the case of recycle or further use of the contaminated process stream, or by upsetting biotreatment or other waste treatment processes, in the case of waste stream treatment or disposal.
Past efforts to remove halogenated organic contaminants from hydrocarbon process or waste streams have focused on the use of catalytic hydrogenation, generally in the presence of a noble metal catalyst, to convert the organic halide to a hydrogen halide which is typically removed and/or recovered by caustic treatment. However, when hydrocarbon streams containing reducible components, i.e., unsaturated and/or oxygenated compounds, are employed, the conditions of the catalytic hydrogenation reaction, which involve the presence of molecular hydrogen or a hydrogen donor and elevated reaction temperatures, typically result in significant conversion of the reducible components to their hydrogenated or reduced form. Further, the use of catalytic hydrogenation to remove organic halide contaminants requires a more complicated and expensive process in terms of reactants, equipment and process controls than would otherwise be desired. This is because the catalytic hydrogenation reaction requires large quantities of expensive hydrogen reactant and must be closely controlled in terms of reactant ratios, temperatures, times and pressures. Further, the product separation, particularly where gaseous hydrogen halide must be separated from volatile hydrocarbons, can be difficult to accomplish. Finally, in many cases the hydrogenation catalysts are not readily regenerable and therefore must be replaced periodically as their activity falls off.
For example, U.S. Pat. Nos. 3,892,818; 4,8181,368; 4,840,721, 4,902,842; 4,923,590; 5,314,614; 5,316,663 and 5,401,894 all disclose processes wherein an organic halide is removed via reaction with hydrogen in the presence of a hydrogenation catalyst. U.S. Pat. No. 4,925,998 discloses a variation of this general process for dehydrohalogenation of aromatic halides where the reaction with hydrogen is carried out in the presence of a Group VIII metal catalyst and a compound capable of forming alkyl halide under the reaction conditions selected. An alternative technique is disclosed in U.S. Pat. No. 4,618,686 where it is taught that aromatic and alpha-araliphatic halides can be dehalogenated by reaction with a hypophosphite salt in the presence of a hydrogenation catalyst. Other references showing catalytic hydrogenation as a means of dechlorinating organic feedstreams include Ger. Offen. No. 2,127,182 and Japanese Kokai No. 81,133,221.
Other documented efforts in the prior art to remove organic halide contaminants from various hydrocarbon feedstreams include that disclosed in U.S. Patent No. 3,935,295 where an admixture of zinc oxide and a basic compound of calcium with an inert binder is used to remove HCl formed on hydrotreatment of a liquid hydrocarbon feedstock and in U.S. Pat. No. 4,417,091 where a solid absorbent such as silica, alumina, silica-alumina or an activated earth is used to remove fluorine and/or fluorinated compounds from the olefin product produced by oligomerization of monoolefins over a nickel/aluminum halide catalyst containing a Bronstead acid such as trifluoroacetic acid. In at least the first case (U.S. Pat. No. 3,935,295), the adsorption step must be preceded by catalytic hydrogenation to convert any organic chloride present to HCI.
Accordingly it is apparent that a continuing need exists for new methods of removing organic halide contaminants from hydrocarbon feedstreams which avoid the problems associated with the prior art catalytic hydrogenation processes in terms of cost and complexity and which minimize the loss of reducible components present in the hydrocarbon feed. The present invention provides such a process where losses of reducible components are minimized in a simple and cost-effective way using a regenerable solid adsorbent for organic halide contaminants contained in the hydrocarbon feedstream.